This invention relates to a heater assembly for heated tipped tools and its method of manufacture and more specifically to a heater assembly whose resistance value in ohms remains substantially constant throughout its useful life.
It is well known that the electrical properties of resistance alloy conductors vary with the type of alloy used and that the resistance value changes with temperature. It is also known that the resistance of the assembly will vary with a change in the tension of the wire due to thermal shock or with oxidation that forms in the junction between the resistance wire and the lead conductors supplying current thereto or corrosion of the resistance wire itself. Thus, experiments have shown that the total resistance of such prior art heater assemblies utilizing resistance alloy conductors will vary as a result of one or more of the aforementioned factors.
In order to improve electrical contact and reduce the possibility of oxidation forming in the junction between the resistance wire and the lead conductors, the prior art heater assemblies employed the technique of spot welding the two together. This was generally satisfactory in reducing the effects of oxidation, however, the technical problems of spot welding a fine wire 0.009 inch in diameter, for example, to another wire are significant and require expensive, complex machines requiring operation by skilled workers. No satisfactory solution has been found to the problem of changing resistance due to thermal shock or corrosion of the resistance wire itself. The wrapping of the resistance wire with mica or similar insulating-type material has not been shown to solve these problems.
Such variations in resistance would normally not be of serious consequence in normal soldering iron applications, however, when the heater assembly is used to heat the tips of tools used for delicate, precise soldering or desoldering-type applications where the temperature of the tip must be precisely controlled by electronic circuitry, such variations of the resistance of the heater assembly are intolerable.
In addition, because the temperature controlling circuitry associated with each tool is preset to maintain a specific temperature, consistency of resistance between heater assemblies is essential to enable interchangeability of heater assemblies associated with various types of designs of tips.
Applicant has discovered that by connecting the resistance wire to the lead conductors by a pressure contact or junction resulting from lapping one upon the other several times and surrounding the resistance wire on the heater assembly bobbin as well as the junction between the resistance wire and lead conductors with a coating of insulating material, the junctions are sealed against oxidation, the whole assembly is substantially shock resistant, considerably cheaper, and the overall resistance value remains substantially constant during the life of the assembly in contrast to similar assemblies known in the art as aforementioned which are much more expensive due to the use of complex, expensive machines with skilled operators required when spot welding techniques are used.
It is, therefore, the primary object of the present invention to provide a superior heater assembly for heated tipped tools.
It is another object of the present invention to provide a heater assembly whose resistance value remains substantially constant throughout its useful life.
It is yet another object of the present invention to provide a heater assembly which utilizes a ceramic-type coating to seal the assembly from the deleterious effects of the atmosphere such as oxidation and corrosion to thereby ensure constant resistance.
It is a still further object of the present invention to provide a heater assembly wherein the resistance wire is connected by pressure to the conductor wires to provide a junction which when sealed results in an assembly which is superior yet less expensive than those assemblies utilizing spot-welding techniques at such junctions.
These and other objects and advantages will become apparent to those skilled in the art from the following description considered in connection with the accompanying drawings in which a presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawing is for the purpose of illustration and description only, and is not intended as a definition of the limits of the invention.